The Civil Aviation Authority (CAA) has issued guidelines on air travel for people with medical conditions; please see the link provided.
Cardiovascular disease
unstable angina, uncontrolled hypertension, uncontrolled cardiac arrhythmia, decompensated heart failure, severe symptomatic valvular disease: should not fly
uncomplicated myocardial infarction: may fly after 7-10 days
complicated myocardial infarction: after 4-6 weeks
coronary artery bypass graft: after 10-14 days
percutaneous coronary intervention: after 5 days
Respiratory disease
pneumonia: should be ‘clinically improved with no residual infection’
pneumothorax: absolute contraindication, the CAA suggest patients may travel 2 weeks after successful drainage if there is no residual air. The British Thoracic Society used to recommend not travelling by air for a period of 6 weeks but this has now been changed to 1 week post check x-ray
Pregnancy
most airlines do not allow travel after 36 weeks for a single pregnancy and after 32 weeks for a multiple pregnancy
most airlines require a certificate after 28 weeks confirming that the pregnancy is progressing normally
Surgery
travel should be avoided for 10 days following abdominal surgery
laparoscopic surgery: after 24 hours
colonoscopy: after 24 hours
following the application of a plaster cast, the majority of airlines restrict flying for 24 hours on flights of less than 2 hours or 48 hours for longer flights
Haematological disorders
patients with a haemoglobin of greater than 8 g/dl may travel without problems (assuming there is no coexisting condition such as cardiovascular or respiratory disease)